Archive for the category: Reactive nitrogen deposition

R. L. Deusdará^{1 2}, M. C. Forti¹, L. S. Borma¹, R. S. C. Menezes³, J. R. S. Lima⁴, and J. P. H. B. Ometto¹, E. R. Sousa-Neto¹, K. Ribeiro¹

¹ Centro de Ciência do Sistema Terrestre – CCST, sala 5, 3º andar,  Instituto Nacional de Pesquisas Espaciais – INPE, Avenida dos Astronautas, 1758, 12227-010, São José dos Campos, SP, Brasil,

² karinne.deusdara@yahoo.com.br

³ Departamento de Energia Nuclear – DEN, Universidade Federal de Pernambuco – UFPE, Av. Prof. Luiz Freire, 1000, 50740-540, Recife-PE, Brasil

⁴ Universidade Federal Rural de Pernambuco – UFRPE, Avenida Bom Pastor, s/n, Garanhuns – PE, 55292-270, Brasil

Abstract

The aim of this study was to quantify nitrogen inputs by the rainfall, throughfall and stemflow, assessing the canopy role in the nitrogen transfers between atmosphere and soil in a rural tropical semiarid region in the Brazilian Caatinga. Samples were collected during two wet seasons, one during an extremely dry year (2012) and one during a year with normal rainfall (2013). The ionic concentrations of N-NH₄⁺, N-NO₃^–, dissolved organic nitrogen (DON) and dissolved total nitrogen (DTN) was 0.04 and 0.15, 0.07 and 0.10, 0.49 and 0.48, 0.61 and 0.73 mg l^-1 in the rainfall for 2012 and 2013, respectively. The canopy enrichment for DON were 3 times for both wet seasons and for DTN were 3 and 2 times in relation to rainfall values for 2012 and 2013, respectively. There were no differences in N-NO₃^– between rainfall and throughfall. The enrichment for stemflow were 31, 8, 15 and 17 times for N-NH₄⁺, N-NO₃^–, DON and DTN for the wet season for 2013, respectively. We report a low bulk nitrogen deposition during both wet seasons and an estimative of about 2.05 kg N ha^-1 ano^-1. We estimated slightly lower annual inputs than previous global estimates, likely due to the low rainfall depths that occurred during the studied years and the lack of measured data for South America. Our findings contribute to the knowledge of nitrogen deposition in the northeastern Brazil by providing information for this poorly studied tropical and semiarid ecosystem.

Jianlin Shen¹, Deli Chen², Mei Bai², Jianlei Sun², Trevor Coates², Shu Kee Lam², Yong Li¹

¹ Key Laboratory of Agro-Ecological Processes in Subtropical Regions, Institute of Subtropical Agriculture, Chinese Academy of Sciences, Changsha 410125, China (E-mail: jlshen@isa.ac.cn)

² Faculty of Veterinary and Agricultural Sciences, The University of Melbourne, Victoria 3010, Australia (Email: delichen@unimelb.edu.au)

Abstract

We conducted the first study in Australia to measure ammonia (NH₃) deposition within 1 km from a commercial beef feedlot in Victoria. NH₃ concentrations and deposition fluxes decreased exponentially with distance away from the feedlot. The mean NH₃ concentrations decreased from 419 µg N m^-3 at 50 m to 36 µg N m^-3 at 1 km, while the mean NH₃ dry deposition fluxes decreased from 2.38 µg N m^-2 s^-1 at 50 m to 0.20 µg N m^-2 s^-1 at 1 km downwind from the feedlot. These results extrapolate to NH₃ deposition of 53.9 tonne N yr^-1 in the area within 1 km from the feedlot, accounting for 8% of the annual NH₃-N emissions from the feedlot. This high NH₃ deposition rate nearby the cattle feedlot had caused the increase of soil inorganic nitrogen content, especially for NO₃^– (from 33 mg N kg^-1 at 1000 m from the feedlot to 124 mg N kg^-1 at 50 m from the feedlot). Higher N content (4.0% to 5.7%) in the above-ground part of grassland species and high cover rate of single species (e.g. a cover rate of 31% to 42% at 50 to 200 m from the feedlot for Cymbonotus lawsonianus) were found in the grassland transect  to the southeast of the feedlot. Our results suggest that NH₃ deposition is significant nitrogen (N) nutrient input for surrounding croplands and natural ecosystems.

Massimo Vieno¹, Mark Sutton¹, Mathew Heal², Anthony Dore¹, Rachel Beck¹, David Fowler¹, Rognvald Smith¹, and Stefan Reis¹

¹ Natural Environment Research Council, Centre for Ecology & Hydrology, Penicuik, UK, www.ceh.ac.uk

² School of Chemistry, University of Edinburgh, Edinburgh, UK, www.ed.ac.uk

Abstract

An analysis of 12 years of annual nitrogen and sulphur deposition over the UK was carried out comparing atmospheric chemistry transport model (ACTM) results with an observation-derived calculation (CBED). The two deposition estimates agree well for oxidised sulphur, whereas total oxidised nitrogen deposition was underestimated by the ACTM. Possible causes of this discrepancy are the uncertainties of emissions estimates and the simplification in the ACTM aerosols formation. The CBED deposition estimates are less sensitive to uncertainties in the emissions inventory dataset as the UK deposition values are derived from observed deposition and surface concentrations. However, CBED wet deposition may be over-estimated due to dry deposition to the surface of bulk collectors. The UK deposition estimates show a general decline over the 2000-2012 period investigated; for oxidised sulphur ~86 (ACTM) and ~97 (CBED) Gg S yr^-1, for oxidised nitrogen ~29 (ACTM) and ~45 (CBED) Gg N yr^-1, and for reduced nitrogen ~7 (ACTM) and ~5 (CBED) Gg N yr^-1.

Leiming Zhang¹, Irene Cheng¹, Xiaohong Yao²

¹ Air Quality Research Division, Environment and Climate Change Canada, Toronto (leiming.zhang@canada.ca)

² Ocean University of China, Qingdao, China

Abstract

Long-term (1983-2011) air concentrations and annual wet deposition of ammonium and nitrate at 30 Canadian sites were analyzed.  Long-term median atmospheric NH₄⁺ and NO₃^– ranged from 0.1-1.7 and 0.03-2.0 µg/m³ among the sites, respectively.  Median annual wet deposition varied from 0.2-5.8 and 0.8-23.3 kg/ha for NH₄⁺ and NO₃^–, respectively.  Long-term decline in atmospheric NH₄⁺ from 1994-2010 was observed, whereas atmospheric NO₃^– increased from 1991-2001 and then declined from 2001-2010.  Annual wet deposition of NO₃^– decreased at most sites by 0.07-1.0 kg/ha/a. Average gaseous HNO₃ and particulate NO₃^– wet scavenging contributions to nitrate wet deposition were 72±23% and 28±23%, respectively. Gaseous NH₃ and particulate NH₄⁺ contributed 30±19% and 70±19% to wet NH₄⁺ deposition.

Interannual variabilities in atmospheric ammonia during the most recent seven to eleven years were investigated at fourteen sites across North America.  The long-term average of NH₃ ranged from 0.8 to 2.6 ppb among the four urban and two rural/agriculture sites in Canada.  The annual average at these sites did not show any deceasing trend with largely decreasing anthropogenic NH₃ emission.  An increasing trend was actually identified from 2003 to 2014 at one urban site.  In the U.S., average NH₃ from 2008 to 2015 was 2.2-4.9 ppb at three rural/agriculture sites and was 0.3-0.5 ppb at four remote sites.  A stable trend at one and increasing trends at three rural/agricultural sites were identified.  Increasing trends at the four remote sites were also identified.  Changes in NH₄⁺/NH₃ partitioning and/or air-surface exchange process as a result of the decreased sulfur emission and increased ambient temperature were believed to be the causes of NH₃ at some of the sites

Feng Zhou¹, Rong Wang^1,2, Yves Balkanski², Laurent Bopp², Philippe Ciais²

¹ Sino-France Institute of Earth Systems Science, Laboratory for Earth Surface Processes, College of Urban and Environmental Sciences, Peking University, Beijing, 100871, P.R. China, Email: zhouf@pku.edu.cn

² Laboratoire des Sciences du Climat et de l’Environnement, CEA CNRS UVSQ, 91191 Gif-sur-Yvette, France

Abstract

Satellite data reveal a strong link between contemporary oceanic productivity and climate. Models suggest oceanic productivity is reduced in response to enhanced water stratification induced by warming, but do not include the effect of increasing anthropogenic aerosol depositions of nitrogen and phosphorus (AAD). We model the response of oceanic productivity and chlorophyll to AAD, supported by in situ nutrient and chlorophyll measurements. As a result, AAD reduces the sensitivity of oceanic productivity to sea-surface temperature from -15.2±1.8 to -13.3±1.6 Pg C y^-1°C^-1 in the stratified ocean during 1948-2007. The reduction over the North Atlantic, North Pacific and Indian oceans reaches 40, 24 and 25%, respectively. We hypothesize that future reduction of aerosol emissions in response to higher air-quality standards will accelerate the decline of oceanic productivity per unit warming.